Device for commingling slowly flowing liquids



Apnl 14, 1964 J. A. PLATTE ETAL 3,128,993

DEVICE FOR COMMINGLING SLOWLY FLOWING LIQUIDS Filed Jan. 16. 1961 IN VENTORS JEROME 4. PLAITE IQ/ZAMAQO V. WIGHT BY V/CTOR M MARC) United StatesPatent This invention is a device for continuously mixing a liquidreagent with a continuous liquid sample to be analyzed colorimetricallyor by other means.

Continuous colorimetric analyzers have been developed recently formonitoring a source or conduit of water, such as boiler water, to recordits composition with respect to one or more constituents. Measurementsmay be made in terms of parts per billion, parts per million,

or milligrams per liter. It is common for silica, for example, to bedetermined colorimetrically in the range of 0-300 parts per billionparts of water.

One difficult problem in the design of such a precision continuouscolorimetric analyzer is proper mixing of the reagent and sample toobtain a colored solution free of discrete streams, clouds, or the like.Obviously, a results. Especially where results are measured in terms ofparts per billion, the color resulting from addition of the reagent mustbe evenly distributed throughout the sample by the time it reaches thesample cell. For the sake of economy of reagent-and other practicalconsiderations, the flow of sample in continuous colorimetric analyzersis generally very slow, say, in the neighborhood of 5-7 cc. per minute.The flow of reagent is only about 0.3 cc. per minute. The reagent mustnot only be continuously added to the slowly flowing sample in thecorrect proportion, but it must also be evenly distributed throughout.The flow rates of the sample stream and the reagent stream may bemaintained in the correct proportion through the use of known apparatusnot described herein. Our invention is concerned with the introductionof the slowly flowing reagent into the sample stream and distributing itevenly throughout any given section thereof.

A blade-type mixer of any substantial volume cannot be used to mix thereagent with the sample because the continuous sample must be analyzedin the sequence it is drawn from its source; with the slow flow rateinvolved here, serious errors could result from analyzing a sample takenfrom a relatively large mixing chamber. Relatively large mixing chambersof any type are unsatisfactory for the reason that they necessarilydisturb the continuity of the sample. Long and arduous studies ofcoil-type mixers, which do not disturb the sample continuity, have shownthat they do not satisfactorily accomplish the desired result ofhomogeneous mixing. The liquid in a coil tends to move in discretestreams through the entire length of the coil and to form clouds orsimilar curling effects when it enters the sample cell. The coil mixeris designed to utilize differences in specific gravities of the sampleand the reagent solution; in practice, however, these differences arenot great enough to achieve the desired mixing.

We have invented a device which continuously intimately mixes a reagentin the correct proportion in a flowing sample of liquid withoutsignificantly disturbing the order of the flow. Our invention isparticularly suited to the analyzer described and claimed in the patentapplication of Robert H. Luppold, Jr. et al., S.N. 861,- 5 89 filedDecember 23, 1959, and assigned to the assignee herein.

The presently preferred embodiment of our invention 3,128,993 PatentedApr. 14, 1964 .is illustrated in the drawing, which is a side sectionalview of our invention showing the inlets for sample and reagent, and themixing device.

The presently preferred device comprises a sample inlet tube 1, areagent inlet tube 2, a reagent injector 3, a pressure drop chamber 4formed by a large tube section 5, a restricted connecting tube 6, asecond pressure drop chamber 7 formed by a large tube section 8, and arestricted exit 9.

Operation of the device is asfollows:

The sample proceeds through tube 1 preferably at a rate of about 5 or 7cc. per minute. This flow rate may be controlled precisely by a suitablepump or the like. The reagent solution is present in tube 2, where itflows preferably at a rate of about 0.3 cc. per minute or in any desiredproportion to the sample flow. Both of these flow rates are maintainedand/or continuously proportioned by devices not shown. The reagent isforced into reagent injector 3, which intersects tube 1. Being under aslight pressure, the reagent accelerates in reagent injector 3 and isinjected into tube 1 at a velocity somewhat higher than that at which itwas previously traveling. Its velocity is preferably not any greaterthan the velocity of the sample.

Reagent injector 3 has a projected tip 10 extending approximately intothe center of tube 1. We have found that if the tip of reagent injector3 is flush with the wall of sample tube 1, undesirable fluctuations inthe introduction rate of reagent solution will result because of thetendency of the slowly flowing reagent to cling to itself andconsequently project globules into the sample stream. With the use ofour preferred/design, the reagent solution flows steadily into thesample stream in spite of its low velocity. The inner diameter of thepreferred reagent injector tube is about .028.031 inch. Preferably itprojects into the sample tube for a distance about A to about theinternal diameter of the sample tube.

The reagent is not intimately mixed with the sample as it flows throughtube 1. However, the sudden pressure drop in chamber 4 brings about aturbulence which causes the desired mixing of the reagent and sample inthe chamber. On the other hand, the continuity and sequence of thesample is substantially preserved. No still pockets are formed in thechamber. There are no projections, obstructions, blades, or the likewhich could tend to produce an erratic flow. Thus, the recording made bythe automatic analyzer will accurately reflect the concentration of thetested constituent in the correct and undisturbed sequence with relationto time. The inner diameter of tube 1 is in the preferred form A inch.The inner diameter of chambers 4 and 7 are preferably about $1 inch.Thus, the area of a cross section of the chamber is nine times the areaof a cross section of the tube. We find that this is a particularlydesirable ratio in the range of dimensions which are practical forcontinuous colorimetric analyzers.

The flow is restricted again in connecting tube 6 and enters the secondpressure drop chamber 7 to insure complete mixing. The pressure drop inchamber 7 causes the same type of turbulence as in the initial chamber,again mixing the reagent and sample without substantially disturbing theorder of the sample. Turbulence is again caused to some extent upon thesamples entering restricted exit 9. The sample stream is then carried,completely and intimately commingled, and in substantially the sameorder as it was taken from the source to the sample cell where light ispassed through it to determine the depth of color. A particularlydesirable sample cell which is excellent for its ability to preserve theorder of the sample is that described and claimed in Ralph N. Thompsonin US. patent application S.N. 850,-

669, now abandoned, filed November 3, 1959, and assigned to assigneeherein.

Many colorimetric determinations require the addition of more than onereagent to the sample. More than one of the units described herein maybe used sequentially, to introduce a plurality of reagents to the samplestream. Where a time delay is required to complete a reagent reactionbefore the second or other reagent is added, a tube of the proper volumeand length may be inserted between units to provide a time delaydepending on the flow of the sample. More than one injector tube for adesired number of reagents may be connected to sample tube 1 in caseswhere the several reagents may be mixed simultaneously.

Several other variations in construction of our device may be noted,although it should be distinctly understood that our invention is notlimited to these forms. For example, the ratio of the internal diameterof the mixing chamber to the internal diameter of the sample tube mayrange from about 1.5 to 1 to about 4 to 1. The internal diameter of thesample tube may be made considerably smaller than the preferred form ofinch, since the samples velocity may be increased accordingly or asmaller sample may be used. For practical colorimetric analysis, thesample tube should have an internal diameter of less than about /8 inch.It is preferred not to use a sample tube no greater than inch internaldiameter where the preferred ratio of mixing chamber diameter to sampletube internal diameter of 3 to 1 is to be maintained. We need not usetwo mixing chambers as in the illustrated device. One chamber will besuflicient for some applications; or, it may be desired to use three ormore. Other variations will occur to those familiar with the art towhich the invention pertains.

Our invention may, of course, be used for purposes other than mixingreagents and samples for continuous colorimetric analysis. Any othertype of analysis or other process or device requiring the continuousaddition and mixing of a small amount of a slowly flowing liquid in arelatively large amount of another slowly flowing liquid will benefitfrom our invention.

The illustrated device is the presently preferred form.

Other variations and embodiments of our invention may 5 be constructedwithin the scope of the following claims.

We claim:

1. A continuous liquid sample and reagent mixing device comprising:

(a) a sample tube;

(b) a reagent injector tube of smaller internal diameter than saidsample tube, said reagent injector tube projecting through the wall ofsaid sample tube to a point within the interior of said sample tube andhaving an open end whose axis is substantially perpendicular to saidsample tube;

(0) a mixing chamber forming a continuation of the sample tubedownstream from said reagent injector tube, said mixing chambercomprising a short length of tubing having an internal diameter of fromabout two to about four times the internal diameter of said sample tube;and

(a') an exit tube having an internal diameter smaller than that of themixing chamber.

2. A continuous chemical reagent injector for a con- 25 tinuous liquidsampling system comprising:

(a) a sample tube having an internal diameter of from about & inch toabout inch; and

(b) a reagent injector tube having an internal diameter of about A toabout the internal diameter of the sample tube, said injector tubeprojecting into said sample tube to a point from about A to about of theinternal diameter of said sample tube and terminating at an open endwhose axis is substantially perpendicular to said sample tube.

References Cited in the file of this patent UNITED STATES PATENTS Hookeret al. May 14, 1935 Erasmus et a1 Nov. 17, 1959 Ferrari Apr. 19, 1960UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,128,993 April 14 1964 Jerome A Platte et al.

It is hereby certified that err ent requiring correction and thcorrected below.

or appears in the above numbered patat the said Letters Patent shouldread as Column 1, line 26 before "results" insert cloud erratic firstoccurrence, y pattern in the sample cell will produce Signed and sealedthis 4th day of August 1964,

(SEAL) Attest:

ERNEST W. SWIDER' Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A CONTINUOUS LIQUID SAMPLE AND REAGENT MIXING DEVICE COMPRISING: (A)A SAMPLE TUBE; (B) A REAGENT INJECTOR TUBE OF SMALLER INTERNAL DIAMETERTHAN SAID SAMPLE TUBE, SAID REAGENT INJECTOR TUBE PROJECTING THROUGH THEWALL OF SAID SAMPLE TUBE TO A POINT WITHIN THE INTERIOR OF SAID SAMPLETUBE AND HAVING AN OPEN END WHOSE AXIS IS SUBSTANTIALLY PERPENDICULAR TOSAID SAMPLE TUBE; (C) A MIXING CHAMBER FORMING A CONTINUATION OF THESAMPLE TUBE DOWNSTREAM FROM SAID REAGENT INJECTOR TUBE, SAID MIXINGCHAMBER COMPRISING A SHORT LENGTH OF TUBING HAVING AN INTERNAL DIAMETEROF FROM ABOUT TWO TO ABOUT FOUR TIMES THE INTERNAL DIAMETER OF SAIDSAMPLE TUBE; AND (D) AN EXIT TUBE HAVING AN INTERNAL DIAMETER SMALLERTHAN THAT OF THE MIXING CHAMBER.